Corrosion restraining compositions



United States Tatent O 3 277 011 CORROSION RESTIiAII IING COMPOSITIONSEric Milton Chadwick and Richard Stanley Moreton, Manchester, England,assignors to Imperial Chemical Industries Limited, London, England, acorporation of Great Britain No Drawing. Filed July 27, 1964, Ser. No.385,450 Claims priority, application Great Britain, Aug. 22, 1963,33,303/ 63 8 Claims. (Cl. 252-149) This invention relates to corrosionrestraining compositions and more particularly it relates to liquidcompositions for restraining the corrosion of ferrous metals in acidpickling baths.

Ferrous metals, such as steel, which are subjected to working atelevated temperatures during the course of manufacture become coatedwith a layer of oxide impurity, often referred to as mill scale. Formany subsequent processing operations, such as coating or plating, it isnecessary to remove the layer of oxide scale, and it is usual to do thisby treating the metal in a bath of aqueous acid, an operation referredto as acid pickling. The acid commonly used for this purpose issulphuric acid, although other acids such as hydrochloric acid,phosphoric acid and sulphamic acid may be used. Once the layer of oxidescale is removed, the acid is free to attack the exposed metal surfaceand in order to reduce the attack on the metal itself as much aspossible it is advantageous to add a corrosion restrainer to the acidpickling bath.

We have now found that a particularly valuable corrosion-restrainingcomposition for acid pickling baths may be obtained from a mixture ofdi-n-butylthiourea, an amine/alkylene oxide condensate and a propyleneglycol solvent.

Thus according to our invention we provide a corrosion restrainingcomposition which comprises a mixture of 1 part by weight ofdi-n-butylthiourea and from 2 to 5 part-s by weight of an amine/alkyleneoxide condensate as hereinafter defined incorporated with a propyleneglycol solvent as hereinafter defined, the weight of the said solventbeing from 1 to 4 times the weight of the said mixture.

The amine/alkylene oxide condensates used in the corrosion restrainingcompositions of our invention are the condensates of 1 mol. of analiphatic primary amine containing from 8 to 18 carbon atoms or of 1mol. of a mixture of such amines with from 3 to 20 mols. of an alkyleneoxide. The condensates are thus essentially tertiary amines having analiphatic hydrocarbon radical of from 8 to 18 carbon atoms as one of theN-substituents and having as the remaining N-substituents twopolyalkanoxy radicals, or are mixtures of such amines. The aliphaticprimary amines from which the condensates are derived may have saturatedor unsaturated hydrocarbon radicals which include, for example, octyl,decyl, dodecyl, tetradecyl, hexadecyl, octadecyl, octadecenyl,octadecadienyl and octadecatrienyl. Such aliphatic primary amines andmixtures of such amines may be derived, for example, from naturallyoccurring fatty glycerides such as coconut oil, soyabean oil and tallow,which contain mixtures of such saturated and unsaturated hydrocarbonradicals.

The alkylene oxide from which the amine/alkylene oxide condensates arederived may be ethylene oxide or propylene oxide, but is preferablyethylene oxide. The amine/alkylene oxide condensates contain asubstantial proportion of compounds which may be represented by thefollowing formulaice in which R represents a saturated or unsaturatedhydrocarbon radical of from 8 to 18 carbon atoms, n represents one ofthe integers 2 and 3, and p and q independently represent zero or apositive integer although the condensates are not restricted solely tocompounds of this formula. The condensates are obtained by methods al'ready well known in themselves. Depending on the molecular size of thehydrocarbon radical of the amine and the number of mols. of alkyleneoxide used in the prep aration, the condensates may or may not besoluble in water. We prefer that the condensates are soluble in water,but the invention is not limited to water-soluble condensates.

By a propylene glycol solvent we mean a monopropylene glycol, adipropylene glycol, a tripropylene glycol or mixtures of two or more ofthese glycols. Particularly suitable are mixtures of a major proportionby weight of a dipropylene glycol with a minor proportion by weight of amonopropylene glycol.

The corrosion restraining compositions of our invention, as alreadydefined, are obtained from mixtures of 1 part by weight of di-n-butylthiourea with from 2 to 5 parts by weight of the amine/alkylene oxidecondensate. Particularly valuable are those compositions in which about3 parts of amine/alkylene oxide condensate are used for each part ofdi-n-butylthiourea. The mixture is incorporated with from 1 to 4 timesits weight of the propylene glycol solvent. Within these limits theproportion of the solvent to the mixture is not critical, and theformulation may be varied depending on the particular circumstances inwhich the corrosion restraining composition is to be used.

The corrosion restraining compositions of our invention may be preparedby simple mixing of the components optionally followed by heating, forexample, to 50 C. to ensure complete solution.

The corrosion restraining properties of thiourea and its derivatives arealready well known, but the corrosion restraining compositions of ourinvention have very much better corrosion restraining properties thanwould be expected from the known properties of the individualcomponents. Moreover, our compositions have other advantages overcorrosion inhibiting compositons used hitherto. Thus our compositionsare liquid and when they are added to acid pickling baths they readilybecome emulsified and evenly distributed throughout the bath so that themaximum effect is obtained with a minimum usage of agent. The amount ofthe composition which is added to the acid pickling bath may be variedover wide limits but we prefer to add between 0.03% and 0.5% of thecomposition calculated on the weight of acid. Thus in the case ofsulphuric acid we prefer to add between 0.5 lb. and 8 lbs. of thecomposition to 1 ton of 76% sulphuric acid (B.O.V.). This acid can thenbe diluted to any strength required, usually to between 5% and 25%sulphuric acid before use as a pickling medium. The compositions of ourinvention have the further advantage that they remain fluid and pourabledown to quite low temperatures. This is particularly important since insome of the acid pickling plants in which corrosion restrainingcompositions are used it is not always possible to store them in heatedconditions in cold weather. The compositions of our invention remainfluid and pourable at temperatures substantially below that of thefreezing point of water, for example down to temperatures of 12 C. (10F.). Our compositions also have the advantage that they induce foamingin acid-pickling baths, and so reduce acid spray.

The invention is illustrated but not limited by the following examplesin which the parts and percentages are by weight.

Example 1 A mixture of 10 parts of di-nbutylthiourea and 30 parts of thecondensation product of a cocoarnine with 15 mols. of ethylene oxide wasdissolved in 70 parts of dipropylene glycol.

Example 2 A 40 cm. length of bright annealed mild steel strip, 6 mm.wide and 0.3 mm. thick, was immersed in 20% w./w. aqueous sulphuric acidcontaining 0.05% W./w. of the composition of Example 1 for 15 minutes at95 C. and was found to have lost 0.0178 gram in weight. A similar mildsteel strip treated under the same conditions with 20% w./w. aqueoussulphuric acid omitting the composition of Example 1 was found to havelost 1.7740 grams in weight.

What we claim is:

1. A corrosion restraining composition which consists essentially of amixture of 1 part by weight of di-n-butylthiourea and from 2 to parts byweight of an amine/alkylene oxide condensate incorporated with apropylene glycol solvent selected from the class consisting ofmonopropylene glycol, dipropylene glycol, tripropylene glycol andmixtures of said glycols, the weight of said solvent being from 1 to 4times the weight of the said mixture, and said amine/alkylene oxidecondensate having the formula:

in which R represents a radical selected from the class consisting ofsaturated and unsaturated hydrocarbon radicals containing from 8 to 18carbon atoms, and the sum of p and q represents a number selected from 0to 20. 2. A composition as claimed in claim 1 which contains about 3parts by weight of said amine/alkylene oxide condensate for each part ofdi-n-butylthiourea.

- 3. A composition as claimed in claim 1 in which the amine/alkyleneoxide condensate is the condensate of 1 molecular proportion ofaliphatic primary amine containing from 8 to 18 carbon atoms in eachmolecule with from 3 to 20 molecular proportions of ethylene oxide.

4. A liquid corrosion restraining composition which consists essentiallyof a mixture of 10 parts of di-n-butylthiourea and 30 parts of thecondensation product of 1 molecular proportion of a cocoamine with 15molecular proportions of ethylene oxide dissolved in parts ofdipropylene glycol.

5. An acid pickling bath consisting of an aqueous pickling acidcontaining a corrosion restraining composition which comprises a mixtureof 1 part by weight of di-nbutylthiourea and from 2 to 5 parts by weightof an amine/alkylene oxide condensate incorporated with a propyleneglycol solvent selected from the class consisting of monopropyleneglycol, dipropylene glycol, tripropylene glycol and mixtures of saidglycols, the Weight of the said solvent being from 1 to 4 times theweight of the said mixture, said amine/alkylene oxide condensate havingthe following formula:

in which R represents a radical selected from the class consisting ofsaturated and unsaturated hydrocarbon radicals containing from 8 to 18carbon atoms, and the sum of p and q represents a number selected from 0to 20.

6. An acid pickling bath as claimed in claim 5 which contains between0.03% and 0.5% of the corrosion restraining composition calculated onthe weight of acid.

7. An acid pickling bath as claimed in claim 5 in which the aqueous acidis 5% to 25% sulphuric acid.

8. An acid pickling bath as claimed in claim 7 wherein the corrosionrestraining composition is presented in a proportion of from 0.5 lb. to8 lbs. of the said composition to 1,520 lbs. of sulphuric acid.

References Cited by the Examiner UNITED STATES PATENTS 1,797,401 3/1931Calcott et al. 25239l FOREIGN PATENTS 923,865 4/1963 Great Britain.

OTHER REFERENCES Armour Ethoxylated Chemicals, Armour IndustrialChemical Company, April 1963, page 17.

LEON D. ROSDOL, Primary Examiner.

JULIUS GREENWALD, Examiner.

S. E. DARDEN, Assistant Examiner.

1. A CORROSION RESTRAINING COMPOSITION WHICH CONSISTS ESSENTIALLY OF AMIXTURE OF 1 PART BY WEIGHT OF DI-N-BUTYLTHIOUREA AND FROM 2 TO 5 PARTSBY WEIGHT OF AN AMINE/ALKYLENE OXIDE CONDENSATE INCORPORATED WITH APROPYLENE GLYCOL SOLVENT SELECTED FROM THE CLASS CONSISTING OFMONOPROPYLENE GLYCOL, DIPROPYLENE GLYCOL, TRIPROPYLENE GLYCOL ANDMIXTURE OF SAID GLYCOLS, THE WEIGHT OF SAID SOLVENT BEING FROM 1 TO 4TIMES THE WEIGHT OF SAID MIXTURE AND SAID AMINE/ALKYLENE OXIDECONDENSATE HAVING THE FORMULA